Method and device for positioning prestressing hoops

ABSTRACT

In a method of positioning hoops of steel wire or strip for the application of circular prestress to pressure vessels provided at uniform intervals with peripheral support saddles, a winding core is placed between the saddles and the prestressing hoops and is displaced in rotational motion so as to wind the hoops. The device for carrying out the method comprises radial rollers and adjacent axial rollers so arranged as to form a roller track corresponding to the internal diameter of the winding core, at least one pressure roller for displacing the core and the hoop and at least one stationary drum for feeding steel strip.

United States Patent [191 Costes et al.

[451 May 13, 1975 METHOD AND DEVICE FOR POSITIONING PRESTRESSING HOOPS[75] Inventors: Didier Costes; Jack Picaut, both of Paris, France [73]Assignee: Commissariat a IEnergie Atomique,

Paris, France [22] Filed: Feb. 5, 1974 [21] App]. No.: 440,137

[30] Foreign Application Priority Data Feb 6, 1973 France 73.04168 [52]U.S. Cl 29/150; 29/200 B; 29/452 [51] Int. Cl... B23p 13/00; B23p 19/00;B2ld 39/00 [58] Field of Search 29/150, 153, 200 B, 208 B,

[56] References Cited UNITED STATES PATENTS 2,743,514 5/1956 Duecy29/452 3,216,079 11/1965 Keyworth 29/150 X 3,221,401 12/1965 Scott et al29/208 D Primary Examiner-Thomas H. Eager Attorney, Agent, orFirm-Cameron, Kerkam, Sutton, Stowell & Stowell [5 7 ABSTRACT In amethod of positioning hoops of steel wire or strip for the applicationof circular prestress to pressure vessels provided at uniform intervalswith peripheral support saddles, a winding core is placed between thesaddles and the prestressing hoops and is displaced in rotational motionso as to wind the hoops.

The device for carrying out the method comprises radial rollers andadjacent axial rollers so arranged as to form a roller trackcorresponding to the internal diameter of the winding core, at least onepressure roller for displacing the core and the hoop and at least onestationary drum for feeding steel strip.

11 Claims, 6 Drawing Figures METHOD AND DEVICE FOR POSITIONINGPRESTRESSING HOOPS This invention relates to the fabrication ofprestressing hoops by winding and to the prestressing of these latter ona vessel which contains an internal pressure.

It is a known practice to make use of hoops formed by winding unstressedwire or cable followed by tensioning of the hoops by means of radialjacks and wedges. As an alternative to wires or cables, it is also knownto make use of thin steel strip. The superposition of turns of stripaccordingly permits the formation of prestressing hoops of substantialthickness without any need to provide embracing support saddles as inthe case of cables and wires.

By analogy with the known practice adopted for hoops formed by wires orcables, the arrangements contemplated up to the present time in the caseof hoops made of steel strip have consisted in forming these latter insitu by supplying the strip from a cable drum and winding the stripround the cylindrical shell of the vessel which is intended to containan internal pressure. This accordingly entails the need to cause thecable-drum support or frame to revolve about the axis of the cylindricalshell as well as the need to provide a.

substantial clearance space, with the result that difficulties areliable to arise in erection and operation on a construction site.

The primary aim of this invention is to overcome the difficulties whicharise in known methods either at the time of formation of the hoops bywinding or during prestressing of these latter.

To this end, the invention proposes a method which essentially consistsin placing between the support saddles and the prestressing hoops awinding core which is caused to rotate in order to wind said hoops.

The winding hoop can be constituted by a rigid annular band which ismounted around the cylindrical shell by welding.

In a preferred alternative embodiment, the winding core is constitutedby a number of turns of mild steel strip having the same thickness andwidth as the hardened-steel strip of the prestressing hoop to which saidwinding core can be joined by welding unless it constitutes a softenedextremity of the hardened-steel strip.

In order to facilitate winding of said turns of mild steel, provision ismade for preliminary forming at the moment of winding.

It is apparent that the method leads to the preferred use of steel stripwith softened ends. It is in fact an advantage to make use of softenedends for the purpose of welding in end-to-end relation two lengths ofstrip delivered from a drum and thus to permit of practically continuousoperations in which each hoop is wound without any change in thickness.

The advantage of the method in accordance with the invention lies in thefact that steel strip elements for the winding core and the hoop aretaken from stationarilyfixed feed drums.

Positioning of hoops formed in accordance with the method hereinabovedescribed can be carried out at a suitable height after winding andprior to tensioning.

A device for carrying out the method aforesaid is also contemplated bythe invention and essentially comprises radial rollers and adjacentaxial rollers so arranged as to form a roller track which conforms tothe internal diameter of the winding core, at least one actuatingpressure-roller for displacing the strip of the winding core and of thehoop, at least one stationarilyfixed drum for feeding the steel strip.

Provision is made for shaping rollers which serve to facilitate startingof the mild steel strip as this latter undergoes the winding operation.In order to prevent damage to the hardened-steel strip of theprestressing hoop when the actuating pressure-roller is outside, saidroller is provided with a rim of elastic material.

In an alternative embodiment, arrangements are made to couple theprestressing hoops in pairs in order to endow these latter with highertilting inertia. This coupling is carried out at the moment ofprestressing by means of the jacks themselves.

To this end, the bodies of the common jacks are joined together by meansof a bridge which also serves as a support for the two hoops.

Moreover, each jack is fitted with a wedge which is capable of slidingbetween the jack body and the piston, said wedge being subjected by aspring to a tractive effort in the direction of wedging inorder toensure progressive action of the jacks when these latter are actuated inorder to apply tension to the hoop.

The following specification relates to examples of construction whichare described with reference to the accompanying drawings, wherein:

FIG. 1 illustrates a mode of positioning of hoops which have beenprepared in the workshop;

FIG. 2 illustrates another mode of winding hoops placed on a pressurevessel, in which use is made of a drum for delivering wire or strip;

FIG. 3 is a device for winding hoops which are placed on the pressurevessel;

FIG. 4 is a device for the preparation of the wedging element or annularband which serves to support the hoops;

FIG. 5 is a diagrammatic view in sectional elevation showing thecoupling of hoops with interposition of common tensioning jacks;

FIG. 6 is a sectional plan view of FIG. 5.

In FIG. 1, the hoops 1 are fabricated in the workshop by known methodsof winding around an annular band in accordance with the invention,whereupon said hoops are conveyed to a location above the tank 2 anddisplaced vertically in downward motion around the tank to the desiredlevel. It will be noted that, after fabrication, the strip-steel hoop 1has a fairly high degree of rigidity, especially with respect todeformations outside its plane. As shown at 1a in the figure, the hoopcan thus be readily transported by means of an accompanying supportstructure 3 of relative elementary design. j

From FIG. 2 it is seen that the steel-strip hoops are fabricateddirectly around the cylindrical shell of the pressure vessel by causingthese latter to rotate about their own axes instead of displacing thefeed drum 4. This mode of fabrication in accordance with the inventionresults in a considerable reduction in the clearance space which it isnecessary to provide around the pressure vessel shell. The drum 4 can beplaced at a substantial distance from the hoop and the steel strip issimply intended to be directed along a path which is compatible withfreedom of bending movements.

The hoop 1 shown in FIG. 2 can be constructed at a predetermined heightof the cylindrical shell 2 and then either raised or lowered to itsfinal level. The method of winding in situ can be adopted for anysubsequent repairs while the pressure vessel is in service.

FIG. 3 represents one mode of execution of the winding operation inaccordance with the invention. Radial rollers 5 of slightly conicalshape and capable of free rotation determine a roller track whichsupports the hoop 1 during fabrication. Cylindrical bearing rollers 6having a vertical axis and capable of free rotation are disposed atuniform intervals around the shell 2 and determine the winding diameterofthe wedging element 10. Rotational displacement is carried out bymeans of at least one actuating pressure-roller 7 driven by amotion-transmission system 8 and a motor 9; the pressureroller 7 isplaced externally in oppositely-facing relation to the bearing rollers6. The roller such as 7 which produces direct action on the flexiblestrip element is provided with an elastic covering 7a or a rubber tire(tyre).

In the case of preliminary winding of the hoop on a winding core orannular band 10 (as shown in detail in FIGS. 3 and 4), said annular bandalso rests on radial rollers 5 and is displaced by means of at least oneactuating pressure-roller 7. It is also possible to displace the hoop orthe annular band by means of driving belts in contact with a peripheralzone of its elements (not shown in the drawings). The annular band 10performs a useful function in preventing the flexible element ofhardened steel from being damaged in direct contact with the bearingrollers 6. It is difficult to form said annular band by mechanicalwelding. An easier method of construction consists in forming an initialwinding of metallic strip which is identical in cross-section to thehardened-steel strip employed for prestressing but is formed of steelwhich has higher ductility and tolerance to deteriorative effects. Inorder that the winding operation may readily be started (as shown inFIG. 4), a strip 10 is passed through a set of actuating pressurerollers12 and emerges from these latter with the degree of curvature which isnecessary to ensure that the strip will wind round the cylindrical shell2 of its own accord. The final extremity of said strip is welded to theinitial extremity of the prestressing strip which is not required topass through the rollers 12. The welded joint is clearly ground withvery great care.

The same ductile strip 10 can serve to make joints between a number oflengths of hoop strip which are delivered by different feed drums. Infact, when a plurality of hardened-steel strips are wound one above theother simply by overlaying without welding, correct relative anchoringis thereby achieved, subject to slight local slippage resulting from thewinding action and from the complementary action of clamping collars(not shown); however, the starting end-portions must be ground so as tobe tapered in thickness in order to' prevent stress concentrations inadjacent turns. A predetermined length of ductile strip (not shown inthe drawings) is employed for the purpose of end-to-end welding of twolengths supplied from drums, with the result that each hoop is wound ina practically continuous operation without any change in thickness. Onthe other hand, if a welded joint is not formed, this ductile lengthpermits relative sliding movements which ensure frictional anchoragesand suppress any local damage.

It is known to make use of radial jacks applied against the cylindricalshell of the vessel for the purpose of applying prestress to the hoops.However, this tensioning of the hoops may be accompanied by inclinationor tilting of the hoop as a result ofrotation about the neutral. axis.It should in fact be noted that the hoop and winding core have limitedresistance to tilting during appliw cation of radial prestress when astrip is employed and this entails the need for radial jacks withparticularly rigid guiding. I

In accordance with the invention, stabilitycan be obtained by couplingtogether two adjacent hoops 1m, in as shown in FIG. 5, therebyincreasing the fictitious width of hoop and reducing its tendency. totilt. Furthermore, the center of gravity l5 ofthe transverse sec- I tionof the hoops is located as close as possible to the center of gravity 16and the transverse section of the I jacks l7 and 18 at the level of thepacking-rings of their respective pistons 17a and 18a. Tilting is thusprevented by virtue of the high width-to-heightratio which is thusobtained. To this end, the cylinders 17c and of the corresponding jacksare rigidly coupled together by means of a bridge 27 which also servesas a support for the hoops 1m, 1n. '3

In order that the deformations in the radial plane should be compatible,provision is made for a possibility of vertical sliding motion of thepiston 18a of the 1 lower jack 18 by means of a sheet of slipperymaterial 19 which is interposed for example between the base 181) of thepiston and the bearing zone 20. Wedges 21a 1 I and 21b to which atractive force is applied by a spring 22 ensure progressive Wedgingduring the movement of thrust of the jacks.

In FIG. 6 which is a horizontal sectional view taken along the axis ofthe upperjack 17, there is shown a detail of the device which isdesigned to produce Wedging after application of tension..The jacks suchas 17,or 18' are placed at the bottom of channels 23 formed by bearingribs 24 of concrete. Wedging is carried out after prestressing by thejacks such as 17 and .18, first I by fitting in position a packing piece25 of reinforced concrete and of substantial thickness, then bycompleting with steel plates 26 of smaller thickness inorder to permitadaptation to structural irregularities.

The entire procedure which has been described in y the foregoing canalso apply to windings of wiresand cables. In this case, the annularwinding band must be provided with continuous flanges or uniformlyspaced Y saddles. Saddles are more compatible with the prestressingdeformation but must be completed during the winding operations bycontinuous sectional members which cooperate with the supportingrollers.

What we claim is: I 1. A method of positioning hoops of steel wire orstrip for prestressing a vessel which containsan internal pressure, withinterposition of bearing saddles placed at uniform intervals on theperiphery of the pressure ves- I sel, wherein a winding core is placedbetween the hearing saddles and the prestressing hoops and is driven inrotational motion in order to wind said hoops.

2. A method according to claim. 1, wherein the winding core is formed bywinding one. turn of-mild steel V strip and welding the two ends thereofin abutting rela I tion.

3. A method according toclai m 1, wherein the wind ing core is formed bywindingaplurality of turns of.

mild steel strip having the same thickness as the hardened steel stripof the prestressing hoop. v

4. A method according to claim 3, wherein starting of the winding coreis facilitated by preliminary shaping at the moment of winding.

5. A method according to claim 3, wherein the mild steel strip isconstituted by the softened end of the prestressing strip.

6. A method according to claim 1, wherein the steel strips of thewinding core and of the hoop are taken from stationarily fixed feeddrums.

7. A method according to claim 1, wherein the winding core and the hoopare placed at a suitable height after winding.

8. A device for positioning hoops of steel wire or strip forprestressing a vessel comprising radial rollers and adjacent axialrollers so arranged as to form a roller track which conforms to theinternal diameter of the winding core, at least one actuatingpressure-roller for displacing the core and the hoop, at least onestationarily-fixed drum for feeding the mild steel strip.

9. A device according to claim 8, wherein said device comprises rollersfor shaping the mild steel strip.

10. A device for application of tension to prestressing hoops, whereinsaid device comprises jacks which are common to two adjacent parallelhoops.

1 1. A device according to claim 10, wherein the bodies of the commonjacks are joined together by means of a bridge which serves as a supportfor the two parallel hoops aforesaid.

1. A method of positioning hoops of steel wire or strip for prestressinga vessel which contains an internal pressure, with interposition ofbearing saddles placed at uniform intervals on the periphery of thepressure vessel, wherein a winding core is placed between the bearingsaddles and the prestressing hoops and is driven in rotational motion inorder to wind said hoops.
 2. A method according to claim 1, wherein thewinding core is formed by winding one turn of mild steel strip andwelding the two ends thereof in abutting relation.
 3. A method accordingto claim 1, wherein the winding core is formed by winding a plurality ofturns of mild steel strip having the same thickness as the hardenedsteel strip of the prestressing hoop.
 4. A method according to claim 3,wherein starting of the winding core is facilitated by preliminaryshaping at the moment of winding.
 5. A method according to claim 3,wherein the mild steel strip is constituted by the softened end of theprestressing strip.
 6. A method according to claim 1, wherein the steelstrips of the winding core and of the hoop are taken from stationarilyfixed feed drums.
 7. A method according to claim 1, wherein the windingcore and the hoop are placed at a suitable height after winding.
 8. Adevice for positioning hoops of steel wire or strip for prestressing avessel comprising radial rollers and adjacent axial rollers so arrangedas to form a roller track which conforms to the internal diameter of thewinding core, at least one actuating pressure-roller for displacing thecore and the hoop, at least one stationarily-fixed drum for feeding themild steel strip.
 9. A device according to claim 8, wherein said devicecomprises rollers for shaping the mild steel strip.
 10. A device forapplication of tension to prestressing hoops, wherein said devicecomprises jacks which are common to two adjacent parallel hoops.
 11. Adevice according to claim 10, wherein the bodies of the common jacks arejoined together by means of a bridge which serves as a support for thetwo parallel hoops aforesaid.